Field of the Invention
The present invention relates to an inclination measuring instrument. More specifically, the present invention pertains to an instrument in which a pair of electrodes are located on opposite side surfaces of a spirit level, and the electrodes detect changes in electrostatic capacity between the electrodes caused by the shift of the bubble, the inclination of the glass tube being calculated from said changes.
There is known a spirit level in which the upper inside surface of a glass tube is formed toricly and the amount of shift of a bubble therein is read out through a scale provided on the tube so as to measure the inclination of the ground or a horizontal portion of a structure.
There is also known, as shown in Japanese Patent Disclosure No. 53-59461, an electrostatic capacity system apparatus for measuring inclination, which detects the inclination as an electric signal. The apparatus, as shown in FIG. 7, has a common electrode 81 placed on a lower surface of a tube 80 and two electrodes 82, 84 located on the upper surface of the tube 20 in line with the direction of movement of a bubble 2, so that first and second capacitors are formed by the electrodes 81, 82 and the electrodes 81, 84, respectively. These capacitors are connected with an alternating current bridge circuit, and when the bubble 2 is shifted by changes in the inclination, the inclination is indicated as a differential voltage output of the bridge circuit.
It should, however, be noted that in the conventional apparatus the electrodes are located close to one another, and that consequently resistance and stray capacity form in the capacitors. The resistance and the stray capacity are easily affected by ambient conditions, for example temperature, so that it is impossible to precisely carry out the measurement of inclination thereby.